Condition monitoring refers to the procedures whereby the condition of equipment is generally observed by measuring parameters the changes of which reflect a change in the condition of the equipment. In condition monitoring in general, the condition of equipment is monitored regularly and when the condition changes, a more accurate fault diagnosis can be made. Fault diagnostics again refers to the procedures used to detect and identify a fault and to determine the cause of the fault. The most important function of a fault diagnostics system is to detect the fault reliably and safely as early as possible. Sometimes a fault diagnostics system is programmed to suggest a solution for eliminating the fault detected. The aforesaid principle is also utilized in telemonitoring of the condition and state of elevators and likewise in the determining of the need for preventive maintenance of elevators.
In telemonitoring of the condition and state of elevators, the elevators themselves provide and indication of faults to be expected. Thus, the degree of wear of components can be detected before they break down completely. It is therefore possible to preset a fixed target value for the failure frequency of elevators to measure the reliability and quality of the elevator. For example, the target per annum for each elevator could be set at only one fault interrupting the passenger's elevator journey.
The aim of preventive maintenance of an elevator is to eliminate the deterioration of the condition and performance of the equipment occurring in consequence of environmental effects, use and wear. Environmental factors and harder-than-anticipated use accelerate wear of the elevator and may lead to faults. For example, transporting big and heavy objects on an elevator designed for passenger traffic may result in a loosening of joints, changes of adjustments and impairment of the quality of operation of the elevator. Environmental factors such as dust, dirt, temperature and moisture additionally affect the condition and rate of wear of the elevator. If the elevators are not serviced in time, they may develop faults that either prevent passengers from using the elevator at all or impair the quality of operation of the elevator in a decisive way, e.g. the door operation becomes noisy or too slow. The scheduling of preventive maintenance of elevators has conventionally been done either via periodic visits set on certain dates in the calender or based on the extent of usage.
Prior-art technology is described in published application GB 2226428 (B66B 5/02), from which a telemonitoring and diagnostics system comprising several elevators and their monitoring terminals and a telemonitoring center communicating with them is known. Each elevator monitoring terminal observes the history and state of operation and deviations from the normal state of the elevator and sends the information periodically to the maintenance center, which generates the maintenance commands. This system is used to monitor door faults, door drives, condition of the motor, the stopping position and brakes of the elevator, operation of the control system, rope elongation, etc.
The maintenance center, communicating with the aforesaid elevator monitoring terminals over telephone lines, is provided with a diagnostics program and a monitor for receiving and analyzing the operation data and history. By these means, based on information obtained from the operation history of the elevators, the system tries to prevent faults caused by aging.
The known state of the art is also represented by published application JP228046/1999, which discloses a telemonitoring system for elevators. In this system, information is collected from inside the elevator by means of cameras and microphones, and the information describing the condition of the car is sent to a telemonitoring unit, whereafter a decision making unit makes decisions regarding abnormal conditions. Problem situations detected are reported to the telemonitoring center. In this system, the elevator in which problems have been detected is also sent instructions for coping with the problems. In the system presented in this publication, the cameras and microphones are active even when passengers are present in the elevator.
The problem with prior-art solutions is that the information collected about the elevator is not necessarily always sufficiently accurate, in consequence of which the elevator telemonitoring system may give a false alarm based on an incorrect interpretation.